Greece's Foreign Ministry has said that two new "national marine parks" announced by Turkey in the northeastern Aegean and Eastern Mediterranean are illegal under international law.
In a statement the ministry said the designations extend beyond Turkish territorial waters and infringe on Greece's continental shelf.
Turkish President Recep Tayyip Erdogan signed presidential decrees establishing the two marine parks, published in Turkey's Official Gazette.
Ankara has framed the move as an environmental measure to protect marine biodiversity, but Greek officials say it is designed to advance Turkey's maritime claims in the Aegean and reassert its "Blue Homeland" doctrine, which asserts expansive Turkish jurisdiction over surrounding waters.
The Greek Foreign Ministry said no state may unilaterally establish marine protected areas in international waters under the Law of the Sea, and said the parks are equally unlawful to the extent they overlap with Greece's continental shelf.
The ministry said the designations "produce no legal effect whatsoever" regarding either international waters or Greek sovereign rights, and cannot create facts on the ground.
Greece noted it had previously established its own national marine parks in the Ionian and Aegean seas strictly within its territorial waters, in full compliance with international maritime law.
The ministry said unilateral actions attempting to alter the legal status of maritime zones in the Aegean and Eastern Mediterranean violate international law and undermine efforts to maintain good-neighborly relations between Athens and Ankara. Greece said it would continue defending its sovereign rights "with consistency and determination" in accordance with the Law of the Sea.